Apparatus and method for treating strip



July 12, 1966 w. ZABRISKIE APPARATUS AND METHOD FOR TREATING STRIP 5 Sheets-Sheet 1 Filed May 12 1965 INVEN TOR.

WILLIAM L. ZABR\SKIE HIS ATTORNEY y 1966 w. L. ZABRISKIE 3,

APPARATUS AND METHOD FOR TREATING STRIP Filed May 12. 1965 3 Sheets-Sheet 2 FIG.3

INVEN TOR.

WILLIAM L. ZABRISKIE HIS ATTORNEY y 1966 w. L. ZABRISKIE 3,259,993

APPARATUS AND METHOD FOR TREATING STRIP Filed May 12, 1965 5 Sheets-Sheet 5 I I I l t FlG.8 l I J INVENTOR.

WILLIAM L. ZABRlSKH;

HIS ATTORNEY United States Patent 3,259,993 APPARATUS AND METHOD FOR TREATING STRIP William L. Zabriskie, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed May 12, 1965, Ser. No. 455,195 3 Claims. (Cl. 34-23) This application is a continuation-in-part of my copen'ding application Serial Number 241,101 filed November 23, 1962, now abandoned, which in turn is a continuation of my original application, Serial Number 850,438, filed November 2, 1959, now abandoned and assigned to the assignee of the present application.

This invention relates to a novel and improved apparatus and method for cooling a continuously moving strip of metal and is particularly adapted for use in combination with an annealing furnace for continuously annealing strip steel wherein the apparatus of this'invention would be utilized to cool the strip after it leaves the annealing furnace. While the invention offers particular advantages as means for cooling metal in combination with an annealing furnace, the apparatus and method of this invention may also be utilized in conjunction with other processes and particularly may be utilized to heat instead of cool continuously moving strip material. Accordingly, it should be understood from the outset that in the following description and appended claims, wherever the invention is described in connection with a cooling process, it is to be fully understood that it is intended to in clude the use of the invention in a heating process as well.

A known construction for a tower annealing furnace for continuously annealing strip steel comprises a furnace housing through which an elongated sheet of metal or strip is passed. The furnace is provided with a plurality of respectively associated pairs of upper and lower rolls to support and drive the strip through the furnace in a plurality of parallel, vertically extending loops. This vertical multi-pass arrangement of the furnace permits the length of strip within the furnace to be many times greater than the length of the furnace, thus providing a substantial reduction in the length of the equipment over that required for a single horizontal pass arrangement. After the strip'leaves the furnace, it is necessary to cool the strip in a controlled manner. In some cases it is desirable to cool the strip as quickly as possible from a relatively high to a moderately low temperature. At other times, it may be desirable to cool the strip from a relatively high temperature of around 1000 F. to a moderate temperature of approximately 500 F. and then cool the strip quickly to a relatively low temperature of about 150 F. It is, of course, always desirable to maintain the size and particularly the length of the cooling apparatus as small as possible in order to maintain the plant facility requirement for the over-all installation at a minimum.

One heretofore known arrangement for cooling strip comprises a plurality of vertically arranged parallel cooling structures in which is circulated cooling water to provide heat transfer from the strip by means of radiation. The strip is passed between the coolers in a vertical multpass fashion by means of a structure similar to a tower furnace. The Water cooled radiation type coolers are relatively satisfactory for reducing strip temperature from a high to a moderate temperature in a fairly short length 3,259,993 Patented July 12, 1966 ice of time but are not as satisfactory for quickly reducing the temperature of the stripfrom a moderate to a relatively low temperature. It is not unusual for a strip cooler of this type to have asmany as thirty to thirtyfive passes, thus providing a structure having an undesirably large space requirement.

I Another type of strip cooler is shown in United States Patent No. 2,521,044, issued September 5, 1950, in the names of W. -B. Cooper'and E. J. Seabold. In the apparatus of this patent the strip is passed throughthe cooling section in a vertical multi-pass arrangement. A portion of a strip cooling section comprises a plurality of sets of cooling units spaced longitudinally of the cooling section with each set of units comprising a plurality of units arranged vertically in spaced relation alongside the path of the strip. Each of the cooling units comprises a plurality of cooling coils arranged to provide a large area of cooling surface having'a general plane lying parallel and adjacent to a next adjacent strip. A low pressure rise fan is located adjacent the side of the coils opposite the strip for blowing atmosphere through the coils and toward the strip. With the apparatus of this patent, the strip is cooled by reason of radiation between the strip and the large cooling area presented by the next adjacent cooling coils. Also, the low' velocity cooled atmosphere circulated by the fan effects convection cooling of the strip. While a combination radiation and convection cooler of the type shown in the aforementioned patent may provide a higher heat transfer coeflicien-t than the pure radiation cooler, it still does not provide a sufficiently increased heat transfer coefficient to permit marked increases in strip speed without undesirably increasing the over-all size of the apparatus by the addition of more passes of cooling. Also, the location of a large radiation cooling surface next'adjacent to the strip has the disadvantage of increasing the possibility of atmosphere collapse within the cooling section when the strip movement is stopped for any reason. If the strip is stopped with the heat exchangers of the unit still in operation, the strip and. atmosphere will be cooled quickly, thus tending to reduce the pressure of the atmosphere within the cooling section at a rate greater than make-up atmosphere can be provided so as to tend to create a partial vacuum within the cooling section which may cause structural collapse of the walls of the cooling section. Also, of course, this rapid cooling of the strip tends to cause bluing of the same, resulting in the necessity of later scrapping of the strip within the furnace.

As previously mentioned, with the apparatus of the aforementioned patent, the speed of the strip passing through the cooling section must be kept to a relatively low value-on the order of 200 to 250 feet per minutein order to accomplish the desired reduction in strip temperature within a'section having a length of practical size. This same disadvantage is, of course, present in the pure radiation type cooling apparatus. Also, in an apparatus of the type shown in the Cooper et al. patent, the large discharge area of each cooling unit together with the relatively small inlet areas provided on opposite ends of the discharge area tends to create. a situation wherein the lower unitsfeed atmosphere to the higher units, thus providing a differential pressure vertically in each pass of the cooling section. This chimney effect tends to' cause suction in certain areas of the apparatus,

tending to cause air to be drawn in from outside the apparatus, which, of course, is undesirable. Also, the pumping effect between units and vertically of the apparatus tends to defeat any vertical zoning of temperatures within the furnace, which zoning is desirable for efiicient and predictable operation.

Accordingly, it is the primary object of the invention to provide novel and improved apparatus for heating or cooling continuously moving strip in a controlled atmosphere which will provide a marked improvement in heat transfer coefficient to permit a more rapid heating or cooling rate and thus permit the use of a materially higher strip speed, and which will at the same time provide a substantial decrease in the number of passes required to heat or cool the strip so as to provide a marked improvement in production rate while at the same time obtaining an over-all reduction in apparatus size.

It is a further object of this invention to provide novel and improved strip cooling apparatus of the type described which will effectively prevent atmosphere collapse or strip bluing when strip movement through the apparatus is halted.

It is still another object of the invention to provide novel and improved strip cooling apparatus of the type described which will facilitate installation and maintenance of the apparatus.

In strip cooling apparatus of the type having a housing for containing a controlled atmosphere and having a plurality of rolls for passing strip through the housing in a vertical multi-pass fashion, the objects of the invention are achieved in one embodiment thereof by the provision of a series of atmosphere recirculating units arranged vertically between each pass of strip for the discharge of cooled atmosphere in a high velocity jet stream toward the next adjacent strip. Each jet unit generally comprises a plenum chamber having an orifice discharge opening facing the strip and extending across the full width of the strip. The plenum chamber is in communication with the outlet of a high pressure rise fan and motor unit. The inlet of the fan is in flow communication with inlets to the jet unit which are disposed on opposite sides of the discharge nozzle and in a direction longitudinally of the strip path. The arrangement thus provides a series of jet discharge orifice means located adjacent the plane of the strip and along the path of strip movement for directing high velocity jets of atmosphere against the moving strip together with suction means positioned intermediate the jets and alternately therewith along the path of strip movement to remove atmosphere from the strip and establish atmosphere flow paths substantially parallel to the path of strip movement. Heat exchanger means are provided in each unit for the cooling of atmosphere circulated through the unit. The high velocity flow of atmosphere from the plenum chamber toward the strip moving by the cooling unit is split into two paths by the strip and passes in opposite directions longitudinally of the direction of strip movement and then inwardly of the jet unit through the inlet means for recirculation. For reasons which will be fully explained hereinafter, the jet units are constructed to provide that the velocity of the atmosphere recirculated by each unit, in directions parallel to strip movement, as measured adjacent the inlets to each jet unit, is at least equal to the lineal speed of the strip. The velocity of the gaseousmedium at the point of impingement should be between 5,000 and 12,000 feet per minute. This high velocity jet cooling of the strip permits a reduction of as high as 75 percent in the number of passes required to cool over a particular temperature range than does a conventional pure radiation type cooling apparatus. Also, the lineal strip speed may be increased as much as 400 percent and higher, thus not only reducing the plant facility requirements for the apparatus but markedly increasing the production rate of strip handled by the apparatus. Each jet unit is preferably constructed so that it may be mounted in the housing of the cooling apparatus merely by sliding the unit into or out of the housing in a direction parallel to the general plane of the strip. This plug-in modular structure will, of course, obviously facilitate installation and maintenance of the units although it will be understood that my invention is not limited in its scope to this particular embodiment. A more detailed understanding of the invention as well as additional objects and advantages thereof may be had by reference to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a side elevational View of an exemplary annealing tower incorporating a jet cooling arrangement embodying my invention;

FIG. 2 is an end elevational view of the annealing tower of FIG. 1;

FIG. 3 is a fragmentary elevational view of a jet cooling unit constructed in accordance with my invention;

FIG. 4 is an enlarged exploded perspective view, partly cut away, of the jet cooling unit of FIG. 3;

FIG. 5 is an enlarged fragmentary perspective view of one of the heat exchange units of the jet cooler of FIG. 4;

FIG. 6 is an enlarged fragmentary cross sectional view of the discharge orifice of the unit of FIG. 3;

FIG. 7 is a fragmentary cross sectional view of the means for mounting the unit of FIG. 3 on the housing of FIG. 1;

FIG. 8 is a diagrammatic view illustrating the flow paths of atmosphere discharged from the unit of FIG. 3; and

FIG. 9 is a graph representing the performance obtainable from a jet cool-ing unit of this invention.

With reference to the drawings and particularly FIGS. 1 and 2, an exemplary tower cooling apparatus of a type for which the present invention is adapted for use is shown. The tower comprises a housing 10 constructed to contain a controlled atmosphere and to exclude air from entering within the housing. The housing includes a plurality of pairs of upper and lower driving rolls 12 and 14 with the upper rolls 12 being spaced a substantial distance above the lower rolls 14. As shown in FIG. 2, suitable drive means such as electric motors 16 are supported on the housing 10 and are drivingly connected to the rolls 12 and 14. The strip 18 enters the housing 10 through a suitable atmosphere seal 20 from an annealing furnace and is passed alternately around the upper and lower rolls 12 and 14 which support the strip 18 in a plurality of vertically extending loops to provide the strip with a vertical multi-pass path through the housing -10. The strip leaves the housing 10 through suitable seal rolls 22 which preclude exhausting of atmosphere through the exit opening 2 4 for the strip. Suitable means are provided, but not shown, for introducing and maintaining a proper amount of the controlled atmosphere in the housing 10. In the interest of brevity, further details regarding the specific construction of the housing 10 with respect to such things as the supporting and driving of the strip through the housing as well as the control of strip speed, maintenance of atmosphere conditions, etc., will not be described, inasmuch as such details are not necessary for a full understanding of the present invention and are well known to those skilled in the art.

In accordance with the embodiment of the invention illustrated, a plurality of atmosphere recirculating jet cooling units 30 are supported on each of the opposite sides of the housing 10 in a plurality of horizontally spaced vertical rows. The jet cooling units 30 supported on the side of the housing illustrated in FIG. 1 are arranged in vertical rows each disposed between two next adjacent passes of the strip 18, with the vertical rows of units being horizontally spaced a distance corresponding to the horizontal spacing of next adjacent strip passes.

On the side of the tower opposite that illustrated in FIG. 1, the vertical rows of jet units supported thereon are disposed, as shown in dotted lines in FIG. 1, outwardly of the end passes of the strip 18 as well as between, or in staggered relationship with, the next adjacent pairs of jet units supported on the other side of the tower housing. In this manner a row of jet cooling units 30 is disposed next adjacent each face or side of the strip 18 in each pass of the strip.

The concept of stagger spacing of the jet orifice means on opposite sides of the strip, which is incorporated in the embodiment of my invention set forth herein, is the invention of Mr. William A. Bloon and is described and claimed in United States Patent Number 3,102,009 granted on August 27, 1963, and assigned to the assignee of this application. The stagger spacing concept whereby the jets on opposite sides of the strip are displaced from each other along the path of strip movement and away from direct face to face relationship is an improvement over my invention and the various objects and advantages of this improvement are fully explained in the aforementioned Bloon patent.

With reference to FIGS. 3 to 7, each jet cooling unit comprises a casing 32 provided with a rectangular mounting flange 34 which telescopically fits within a collar or flange 36, such as shown in FIG. 7, and which is provided on the wall of the housing 10. Each mounting flange 34 is joined to the flange 36 on the wall of the housing by welding the outermost edges of the two flanges to provide a gas-tight seal.

With the jet uni-t 30 mounted on the housing as shown in FIG. 2, the portion of the casing disposed to the left of the flange 34 as viewed in FIG. 4 will be disposed within the housing. A pair of Walls or partitions 40, 42 extend longitudinally of the casing and divide it into a central plenum chamber 44 and a pair of inlet chambers 46 disposed on opposite sides of the plenum chamber. As will be apparent from FIGS. 2 and 4, when the jet unit is mounted on the housing 10, the plenum and inlet chambers of the unit will be aligned in a direction extending parallel to the path of strip movement in a next adjacent pass of strip.

To provide for the discharge of atmosphere from within the plenum chamber 44 toward a next adjacent strip, orifice means are provided in each casing 30 and, as shown, is in the form of a narrow elongated slot or nozzle '48 registering with the plenum chamber 44. The slot 48 extends longitudinally of the jet cooler so as to extend laterally of a next adjacent strip and parallel to the general plane of the strip. The length of the slot 48 is preferably at least equal to the width of the strip intended to be cooled so as to assure uni-form cooling across the full width of the strip. In the case of jet cooling units located between next adjacent passes of strip, the casing 30 is provided with two slots 48 on the opposite faces 31 of the casing so as to provide for the simultaneous discharge of atmosphere in opposite directions toward the next adjacent strips. As will, of course, be understood, in the case of the-end units associated with the end passes in the housing, only one slot 43 will be provided inasmuch as these units are operative on only one side of the stri'p in the next adjacent pass. As best shown in FIG. '6, in order to enhance the nozzle characteristics of each slot 48, the casing 32 is provided with diverging lips 50 extending from the longitudinal bordering edge portions of each slot 48 and inwardly of the plenum chamber 44. A channel brace 52 supports each lip 50 in the desired angular relation to the face of the casing 32.

With reference to FIG. 4, each of the inlet chambers 46 is provided with an inlet opening 54 located in the side of the casing 32 and facing in a direction parallel to the next adjacent faces 31 of the casing and away from the plenum chamber 44. Thus, the inlet openings 54 will face in a direction parallel to the direction of strip movement and, as shown, will be in a general plane extending at right angles to the general plane of the jet discharge orifice means 48. A pair of heat exchangers 56 are supported within the casing 30 alongside the inlet openings 54 so as to be in heat exchange relation with atmos'hpere passing through the inlet chambers. As best shown in FIG. 5, each heat exchanger 56 comprises a plurality of finned tubes 58 through which may be circulated cooling water. As will be readily apparent to those skilled in the art, other suitable heat exchanger means could be employed for cooling purposes. Further, where the jet unit is to be used for heating rather than cooling, heated water or steam could be passed through the finned radiators 58 or other suitable heating means could be employed.

In order to provide for circulation of atmosphere through the jet unit, a fan and motor unit 60 is supported on each casing 30 and comprises an electric drive motor 62 and a high pressure rise fan drivingly connected to the motor. In the specific embodiment shown, the fan is a radial flow fan comprising a fan housing 64 and radial fan blades 66. As shown in FIG. 4, the fan is provided with an axial inlet 68 which communicates with the inlet chambers 46 in the casing. The fan is further provided with an outlet '70 communicating 'with the plenum chamber 44. As can be seen in FIGS. 1 and 2, when the jet cooling unit is mounted in place on the housing 10, the fan and motor unit 60 will be disposed externally of the housing where it will be shielded from direct contact with the heat within the tower and further where it is readily accessible for maintenance.

In the operation of a tower cooling apparatus incorporating the present invention, energizing of the drive motor 62 will cause atmosphere to be drawn in through the inlet openings 54 and then through the fan and into the plenum chamber 44 for high velocity discharge through the nozzle or nozzles 48. Since the plenum chamber 44 and inlet chambers 46 are aligned in a direction parallel to the path of strip movement, the discharged atmosphere, as it approaches the strip 18, will, as shown in FIG. 8, split into two paths and flow in opposite directions longitudinally of the strip for recirculation into the inlet openings 54 of the cooling unit. As the atmosphere is recirculated through the jet cooler by the fan, it will, of course, be cooled by the heat exchangers 56. As shown in FIG. 8, the spacing of the inlet openings 54 a substantial distance from the orifice 48 and in a direction parallel to the direction of strip movement provides a high velocity flow of atmosphere in opposite directions longitudinally of the strip for a substantial distance. Inasmuch as the next adjacent coolers in each vertical row provide a similar flow of atmosphere, there will be provided a high velocity flow of atmosphere longitudinally over the strip in each pass but, of course, with the flow being divided into a plurality of zones spaced vertically along each pass.

One of the primary resistances to heat transfer from the strip'to the cooled atmosphere circulated by the cooling units is provided by a boundary layer of hot atmosphere which is carried along by the fast moving strip. One of the advantages of the present invention is that the high velocity or jet discharge of cooled atmosphere from the orifices 48 penetrates this boundary layer of hot atmosphere and reduces the thickness and temperature of this layer, thus bringing the cooled atmosphere into improved heat transfer relation with the strip. In order to achieve this boundary layer removal, it is necessary that the cooled atmosphere passing along the strip have a momentum at least equal to the momentum of the boundary layer. 'It'may thus be said that the velocity of the circulating atmosphere must at least equal the velocity of the boundary layer, which for all intents and purposes will be the lineal speed of the strip. Since the velocity of the circulated atmosphere will be reduced as it passes along the strip in a direction opposite that of the strip movement, it is important, in order to achieve the marked improvements offered by this invention, including the substantial elimination of the pumping effect between adjacent jet cooling units caused by the movement of the strip, that the velocity of the atmosphere in directions parallel to the strip movement and as measured adjacent both inlet openings 54, be at least equal to the velocity of the boundary layer carried by the strip or, in other words, at least equal to the speed of the strip.

The graph presented in FIG. 9 illustrates the marked improvement obtainable by the use of the present invention. The curve of the graph is based upon a tower cooling apparatus such as shown in FIG. 1 incorporating jet cooling units of the type shown in FIG. 4 and utilizing the cooling method described herein. The conditions of operation are a strip speed of 1500 feet per minute, with the strip having a thickness of ten thousandths of an inch and a width of thirty inches. The temperature drop of the strip is from 600 F. to 225 F. The orifices 48 alongside each side of the strip are spaced apart vertically a distance of approximately seven feet. An exemplary number and arrangement of such jet units is forty units arranged in five vertical rows of eight units each to provide four passes of strip with a total of sixtyfour jets acting on the strip. The width of each slot 48 is selected to be 0.8 inch, with the length of the slot being approximately 36 inches and the width of each opening 54 is approximately 11 inches, with the length of the opening being approximately 47 inches. The solid line portion of the curve of FIG. 8 represents, for the above described jet cooling unit structure and arrangement, the predicted average heat transfer coefiicient obtainable from a jet discharge unit over a range of jet discharge velocities of from 8,000 feet per minute to 18,000 feet per minute. The average heat transfer coefficient is defined as the B.t.u.s of cooling provided by each jet per hour per square foot of strip per degree Fahrenheit of temperature difiference between the strip and the cooling atmosphere. The average heat transfer coefficient at zero velocity is that which is obtainable with a purely radiation type cooler. The dotted line portion of the curve is a logical extrapolation of the solid line curve to the heat transfer coefiicient value for the purely radiation type cooler. It can be seen that a marked rate of increase in the average heat transfer coefliicient occurs around a jet discharge velocity of approximately 5,000 feet per minute and that at a jet velocity above 12,000 feet per minute a marked levelling off in the average heat transfer coefficient occurs. Thus, the range between 5,000 and 12,000 feet per minute was found to be a critical range.

With the jet cooling structure and arrangement forming the basis of the curve of FIG. 9, it is to be expected that the atmosphere velocity at the inlet openings of the unit will be on the order of to percent of the discharge velocity at the orifices. Thus, in order to provide an atmosphere velocity at the inlet openings which is at least equal to the strip speed of .1500 feet per minute, the jet discharge velocity at the orifice would have to be on the order of 4300 to 5000 feet per minute. An appreciable improvement in rate of increase in heat transfer coefficient can be noted in the jet discharge velocity of from 7,000 to 12,000 feet per minute, iwhich corresponds to atmosphere velocity at the inlet openings of from approximately 2300 to 3900 feet per minute or from approximately 1.5 to 12.5 lineal strip speed. At these higher velocities it is believed that the boundary layer of hot atmosphere carried by the strip is removed to a greater extent while at the same time cooling atmosphere is circulated relative to the strip at a greater rate, thus increasing the over-all heat transfer relationship between the strip and atmosphere in a non-linear manner.

As a specific example of the advantages obtainable through the use of the present invention, a typical purely radiation cooler installation for cooling strip from 900 F. to 225 F. required an installation approximately 1500 feet long involving thirty passes of strip. Eighteen passes were required to bring the strip temperature slowly from 900 F. to 460 F. In view of the desire to maintain this slow temperature drop in the system, eighteen passes of pure radiation cooler were retained. The remaining twelve passes of radiation cooling were replaced with four passes of a jet cooling arrangement constructed in accordance with this invention to bring the strip temperature from 460 F. to 225 F. Additionally, two passes of jet cooling were required to bring the strip temperature from 225 F. to F. It will, of course, be recognized that it is much more iditficult to extract heat from the strip in the lower temperature ranges than it is in the higher ranges. It was estimated that if it had been desired to replace the initial eighteen passes of radiation cooling with the faster jet cooling apparatus, only two passes of jet cooling would have been required rather than the eighteen passes of radiation cooling in order to achieve the same reduction in strip temperature.

The marked reduction in the number of passes provided by the jet cooling apparatus of this invention obviously results in a marked reduction in the space requirement for the apparatus over that required for pure radiation cooling. In this connection, a reduction in length of apparatus of 75 percent would not be unusual. Additionally, there will, of course, be an increasingly less number of rolls and associated structure, which more than offsets any additional cost involved in the jet cooling apparatus. Further, the most frequent strip breakage in a cooling apparatus occurs as a result of the rolls, which may cause wrinkles in the strip which when the strip is then bent over succeeding rolls causes breakage. Obviously, with the marked reduction in the number of rolls in the over-all apparatus, the percentage of breaking or cracking of the strips is substantially reduced if not essentially eliminated.

An additional advantage of the present invention is provided by reason of the shielding of the heat exchangers from direct radiation relationship with the strip. In a pure radiation cooling apparatus, if the strip movement should be stopped, the strip will be cooled by radiation by the next adjacent water cooled surfaces. This will result in a drop in the temperature and pressure of the atmosphere contained within the apparatus at a rate which may be suflicieutly rapid that the apparatus for providing make-up atmosphere cannot provide atmosphere at a sufliciently fast rate. The result would be a negative pressure within the enclosure which can cause severe buckling of the walls of the enclosure or in a severe case might cause an implosion. In the apparatus of the present invention, if strip movement should be stopped, there will be some convection cooling of the atmosphere by the heat exchanger, but there will be no radiation cooling of the strip by the heat exchangers because of their being shielded from the strip. The convection cooling of the atmosphere by the heat exchangers will not, however, be at a sufficiently high rate that the normal atmosphere make-up apparatus cannot maintain the proper atmosphere pressure within the enclosure. Thus, atmosphere collapse is effectively prevented. The shielding of the heat exchangers from the strip will, when strip movement is stopped, preclude sufficiently rapid cooling of the strip to cause bluing thereof, which was another disadvantage of the purely radiation type coolers or of any cooler in which a large radiation surface is in direct radiation relationship with the strip. The bluing of the strip would, of course, result in scrapping of that portion of the strip affected.

The relatively large size of the inlet openings of the jet coolers constructed in accordance wit-h this invention as compared to the area of the orifice outlets from the discharge plenum chamber assures that one unit will not feed atmosphere to another unit spaced thereby as might be caused inlow discharge velocity systems having large outlet openings; There is thus avoided any chimney effect in each vertical row of jet units which would tend to cause a large. differential pressure through the system which might cause air to be sucked in through the housing atthe low pressure point. Furthen the avoidance of any vertical pumping from one unit to the next in any vertical row of units provides vertical zoning within each row. The vertical zoning provided will permit more accurate control of temperature drops in the strip from unit to unit as it passes through the cooling tower, thus providing more accurate metallurgical control of the strip.

Jet cooling apparatus constructed in accordance with the above-described embodiment of this invention also provides for easy installation and maintenance of the units, inasmuch as each unit is merely slipped into the housing in plug-in fashion by moving the unit parallel to the general plane of the strip in the respective paths or, in other words, by moving the unit parallel to the axis of the drive rolls. As will be apparent, whenever it is desired to remove one of the units for replacement or maintenance, it is a simple matter to merely pull the unit out and replace it with another unit. The replacement may be accomplished in a minimum of time and with a minimum of effort so that the production rate of the cooling tower is not impaired. The maintenance of the motors and fans of the units is facilitated by the location of these units outside of the housing where they can easily be serviced or replaced. Additionally, the shielding of fans and motors from the interior of the housing and the high temperatures therein provides for longer service life of these components as well as for more efficient operation. The individual motor drive for each unit provides optimum control of the system, inasmuch as if desired the discharge velocity of the individual units may be varied to accomplish any desired temperature gradient through the cooling tower.

It will be seen from the foregoing that I have provided an improved method and apparatus for heating or cooling moving metal strip in which a recirculating atmosphere in the form of high velocity jets is directed against the moving strip with suction means being positioned in between the jet orifice means and alternately therewith along the path of strip movement to remove atmosphere from the strip and to establish atmosphere flow paths in directions substantially parallel to the path of strip movement, with the atmosphere being continuously recirculated through series flow heat exchanger means. My invention is particularly applicable to strip metal annealing furnaces and as I have pointed out above, provides marked improvements and advantages in such applications over methods and apparatus heretofore known.

Whilethe invention has been described in terms of the specific embodiment shown, it will, of course, be understood that various modifications and alterations may be made in the structure shown Without departing from the scope of the invention and that the method disclosed herein for heating or cooling moving strip metal may be practiced with apparatus other than that set forth. Particularly, it is emphasized that the units may be utilized for heating as well as cooling and in all cases in the foregoing description and following claims where the apparatus and method are described in terms of cooling it is to be understood that it is intended to also include heating.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A continuous process strip annealing furnace comprising:

(a) a furance housing having means comprising spaced apart rolls for supporting in a vertically oriented span moving strip metal passing therethrough, said moving strip metal having an atmosphere boundary layer adjacent thereto,

(b) at least a pair of plenum chambers in said furnace eous medium flow path from said orifice means tosaid inlet means for each plenumchamber,

(f) a fan means connected to each of said plenum chambers for pressurizing the gaseous medium within said plenum chambers,

(g) the design capacity of said fan means being sufficient to produce a pressure level in said plenum chambers which will yield a jet discharge velocity at said orifice means between 5,000 and 12,000 feet per minute to impart a momentum to said gaseous medium moving against said strip metal that exceeds the momentum of the boundary layer,

(h) means connecting each inlet means back to the fan means associated therewith to establish separate recirculating flow paths for each plenum chamber,

and

(i) heat exchanger means connected in series flow relationship with the fan means in said recirculating flow paths of each plenum chamber.

2. A continuous process method of heating or cooling strip metal comprising:

(a) continuously moving said strip metal through a housing, said moving strip metal having an atmosphere boundary layer adjacent thereto.

(b) exposing for treatment a portion of said moving strip between support points in said housing,

(c) directing a plurality of jets of a gaseous medium from orifices against both sides of said strip at selected and spaced apart areas along said expose-d portion at a discharge velocity between 5,000 and 12,000 feet per minute to impart a momentum to said gaseous medium against said moving strip metal that is greater than the momentum of said boundary layer,

(d) removing said gaseous medium from said strip at points in between said selected areas of jet impingement in such a manner as to establish flow of said gaseous medium along said strip from the areas of impingement to the points of removal in directions substantially parallel to the path of strip movement, and

(e) continuously recirculating the gaseous medium removed from the strip through heat exchanger means.

3. A continuous process strip furnace comprising:

(a) a furance housing having means comprising spaced apart rolls for supporting moving strip metal therein,

(b) a plurality of atmosphere recirculating jet discharge units supported on said main housing alongside the path of the strip and positioned on opposite sides of the plane of said strip,

(c) each of said discharge units having formed therein a plenum chamber disposed at least partially within said housing and extending adjacent the plane of the strip path,

(d) orifice means in each plenum chamber for discharging atmosphere at a velocity between 5,000 and 12,000 feet per minute against said moving strip to cause the jet at the point of impingement against the moving strip metal to split into two streams flowing in opposite directions along the strip metal from the point of impingement.

(e) a separate fan means connected to pressurize each of said plenum chambers,

(f) at least one enclosed inlet chamber formed in each 1 1 of said jet discharge units positioned on opposite sides of said plane of said strip and said at least one enclosed inlet chamber communicating with one of said fan means and the interior of said furnace hous- (g) each of said inlet chambers being aligned with respect to the path of strip movement to form essentially separate atmosphere flow paths from said orifice means to said inlet chambers, and

(h) heat exchanger means connected in series flow relationship with each of said fan means.

References Cited by the Examiner UNITED STATES PATENTS Wilckens 34227 X Dunakin et al. 34-156 X Vaughan et a1 34159 X Gardner 34-122 FREDERICK L. MATTESON, IR., Primary Examiner.

10 WILLIAM F. ODEA, Examiner.

C. R. REMKE, Assistant Examiner. 

2. A CONTINUOUS PROCESS METHOD OF HEATING OR COOLING STRIP METAL COMPRISING: (A) CONTINUOUSLY MOVING SAID STRIP METAL THROUGH A HOUSING, SAID MOVING STRIP METAL HAVING AN ATMOSPHERE BOUNDARY LAYER ADJACENT THERETO. (B) EXPOSING FOR TREATMENT A PORTION OF SAID MOVING STRIP BETWEEN SUPPORT POINTS IN SAID HOUSING, (C) DIRECTING A PLURALITY OF JETS OF A GASEOUS MEDIUM FROM ORIFICES AGAINST BOTH SIDES OF SAID STRIP AT SELECTRED AND SPACED APART AREAS ALONG SAID EXPOSED PORTION AT A DISCHARGE VELOCITY BETWEEN 5,000 AND 12,000 FEET PER MINUTE TO IMPART A MOMENTUM TO SAID GASEOUS MEDIUM AGAINST SAID MOVING STRIP METAL THAT IS GREATER THAN THE MOMENTUM OF SAID BOUNDARY LAYER, (D) REMOVING SAID GASEOUS MEDIUM FROM SAID STRIP AT POINTS IN BETWEEN SAID SELECTED AREAS OF JET IMPINGEMENT IN SUCH A MANNER AS TO ESTABLISH FLOW OF SAID GASEOUS MEDIUM ALONG SAID STRIP FROM THE AREAS OF IMPINGEMENT TO THE POINTS OF REMOVAL IN DIRECTIONS SUBSTANTIALLY PARALLEL TO THE PATH OF STRIP MOVEMENT, AND (E) CONTINUOUSLY RECIRCULATING THE GASEOUS MEDIUM REMOVED FROM THE STRIP THROUGH HEAT EXCHANGER MEANS. 